1. Field of the Invention
The invention relates to a method for drilling shaker bores into the cooling channel of a single-part piston.
2. The Prior Art
A single-part piston with a cooling channel is described in International Patent Application No. PCT/EP02/02381. In the piston shown in this application, the bosses of the gudgeon pin and the elements of the piston shaft are connected with the piston head via a substantially ring-shaped tie-up. Although this piston has a recess extending fully around below the cooling channel, there is no known method that would permit producing shaker bores in the cooling channel of the one-part cooling channel-piston as known from the prior art cited above that extend in the direction of the piston crown in order to enhance the cooling of the piston crown.
Producing such shaker bores in a multipart cooling channel-piston is described in German patent application DE 102 44 512.5, which is comprised of a bottom part and a top part of the piston, with a cooling channel that is open downwards, by drilling such shaker bores into the cooling channel in the direction of the piston crown before the upper part of the piston is mounted on the top part of the piston, whereby the cooling channel is then sealed as well.
It is therefore an object of the invention to provide a method that permits drilling shaker bores into the cooling channel of a single-part piston where the gudgeon-pin bosses and elements of the piston shaft are mechanically tied to the upper part of the piston for stability reasons, for the purpose of enhancing the cooling of the piston crown.
This object is accomplished by a method for drilling shaker bores into a cooling channel arranged on the side of the piston head facing away from the piston crown of a single-part piston, wherein gudgeon-pin bosses, each having a gudgeon-pin bore and piston shaft elements, are molded onto the side of the piston head facing away from the piston crown via a tie-up substantially extending fully around. In the method according to the invention, passage bores are drilled into the tie-up coaxially with the shaker bores to be drilled into the cooling channel. A drilling bit having a diameter smaller than the diameter of the passage bore is inserted into the passage bores. The corresponding shaker bore is drilled into the underside of the piston head with the drilling bit inserted in the respective passage bore.
Preferably, at least a part of the axes of the shaker bores extend parallel with the axis of the piston, or at an acute angle in relation to the axis of the piston. The shaker bores preferably have a cylindrical shape or the form of an oblong hole and are radially symmetrically and/or asymmetrically distributed over the circumference of the cooling channel.
An alternative embodiment of the process is as follows: In a first production step, passage bores are drilled with a first drilling bit into the tie-up and the shaker bores are produced in the cooling channel. In a second production step, using a drilling bit with a diameter larger than the one of the first drilling bit, the passage bores are enlarged and the burrs of the shaker bores are subsequently removed.